There are 180.9 million base pairs on chromosome 5 that make up 923 genes. Chromosome 5 is one of the largest human chromosomes but has a relatively low gene density owing to significant proportions of the chromosome that are non-coding.
Sixty-six genes on chromosome 5 have been identified as involved in human disease if they become mutated and fourteen diseases are thought to be related to chromosome 5 but have yet to be mapped to specific genes.
The types of gene alterations that can occur on chromosome 5 include:
- Deletions – A deletion is a mutation where a sequence of DNA is missing.
- Insertion – An insertion mutation is the addition of one or more base pairs to a segment of DNA.
Two examples of the conditions caused by chromosome 5 gene mutations are Cri-du-Chat syndrome and familial adenomatous polyposis. These are both examples of deletion mutations.
This condition is caused by a deletion in the end portion of the short (p) arm of chromosome 5, written as 5p- (or 5pminus to indicate the deletion). The symptoms of Cri-du-chat are thought to be caused by the loss of multiple genes in this area, although these genes have not yet been specifically identified.
Researchers have found, however, that the larger the deletion, the more severe certain symptoms such as developmental delay tend to be. Researchers have also determined certain areas of the short arm on chromosome 5 that appear to be linked to specific features of the condition such as the cat-like cry after which the condition is named and microcephaly (small head).
Familial adenomatous polyposis
This condition is caused by a deletion mutation of a gene on the long or “q” arm of chromosome 5 that codes for a tumor suppressor protein called adenomatous polyposis coli (APC). Usually APC is involved in how a cell divides and where it moves to. The most common mutation in familial adenomatous polyposis involves the deletion of five base pairs which gives rise to an abnormally short and inactive APC protein that cannot suppress the proliferation of cells. This leads to the formation of thousand of polyps that are potentially cancerous in the rectum and colon which may need to be removed. The condition is also known of as deletion polyposis.